1. Field of the Invention
This invention relates to an air intake of an aircraft nacelle that incorporates a reinforced lip with a Joule-effect defrosting system.
2. Description of the Related Art
An aircraft propulsion system comprises a nacelle in which a power plant is arranged in an essentially concentric manner.
As illustrated in FIG. 1, at the front, the nacelle comprises an air intake 10 that makes it possible to channel an air flow in the direction of the power plant 12. It comprises a lip 14 whose surface that is in contact with the aerodynamic flows is extended on the inside of the nacelle by an inside wall 16 that borders a pipe and on the outside of the nacelle by an outside wall 18.
The air intake 10 is connected to the power plant 12 at a junction surface 20 by any suitable means. The junction surface 20 is essentially planar and perpendicular to the longitudinal axis of the nacelle.
On the structural plane, the air intake 10 comprises a first frame called a front frame 22 that connects the inside wall 16 and the outside wall 18 and that with the lip 14 borders an annular pipe 24 as well as a second frame called a rear frame 26 that connects the inside wall 16 and the outside wall 18 close to the junction surface 20 of the power plant.
Relative to the rear frame 26, the latter ensures the uptake of flexural forces, rotational forces, etc., that are applied to the air intake, such as, for example, the weight of the air intake, and the forces induced by the aerodynamic flows. This rear frame 26 is arranged in a plane that is essentially perpendicular to the longitudinal direction of the nacelle.
A rear frame is described in particular in the document FR-2,904,604.
Relative to the front frame 22, at the inside wall, the latter comprises an edge 28 that is curved toward the rear of the nacelle against which an edge of a panel that forms the lip 14 and an edge of another panel 30 that forms the inside wall 16 are flattened, whereby said edges are placed end-to-end. Advantageously, the panel 30 ensures the acoustic treatment and comprises an alveolar structure, imparting a certain rigidity thereto.
In addition, at the outside wall 18, the front frame 22 comprises an edge 32 that is curved toward the rear of the nacelle, against which at least a portion of the panel that forms the lip is flattened. According to a first variant that is illustrated in FIG. 1, the outside wall 18 is formed by a panel 34 that is independent of the panel that forms the lip 14. In this case, the adjacent edges of the panel 34 and the panel that forms the lip 14 are placed end-to-end and flattened against the curved edge 32. The panel that forms the lip 14 is generally metal in order to be compatible with a system for treating frost or ice, using the hot air that is provided at the air intake and the panel 34 made of composite material to reduce the on-board weight.
According to another variant that is illustrated in FIG. 2, the panel that forms the lip 14 can extend beyond the front frame 22 and extend up to the rear frame 26 in such a way as to form the outside wall 18 as well. Relative to the variant that is illustrated in FIG. 1, this solution makes it possible to improve the aerodynamic characteristics by eliminating the junction zone between the panels placed end-to-end that forms a step that can produce perturbations in the air flows. When the panel is metal and the air intake comprises a defrosting system that uses hot air, for example, this solution makes it possible to increase the surface that is treated on the defrosting plane using the thermal conductivity of the panel. However, this solution has the drawback of increasing the on-board weight.
Even if the panel that forms the lip 14 extends beyond the front frame 22 and extends up to the rear frame 26 in such a way as to also form the outside wall 18, the presence of a front frame 22 is essential because the latter makes it possible, on the one hand, to border an annular pipe for channeling the hot air that is used for defrosting, and, on the other hand, to ensure the mechanical strength by forming a second barrier behind the lip in the event of a bird strike.
As far as defrosting is concerned, there is another solution that does not use hot air, consisting in connecting electrical resistors 36 at the skin that forms the lip. These electrical resistors come in the form of elements made of conductive material that are arranged in a longitudinal direction and are connected to one another in a mounting in series or in parallel electrically.
According to one embodiment, the electrical resistors are flattened against the inside surface of the panel that forms the lip 14 of which the other surface is in contact with the aerodynamic flows.
Even if this type of defrosting does not use hot air, the front frame 22 is, however, necessary for ensuring the mechanical strength.
According to another aspect, the lip 14 experiences numerous small impacts that can generate delamination phenomena between the panel that forms the lip 14 and the electrical resistors 36, in particular in the impact zone. The delamination phenomena lead to the appearance of an air knife between the electrical resistors 36 and the panel that forms the lip 14 that disrupts the defrosting. Actually, this air knife generates a superheating of the electrical resistor(s) 36 at the delamination zone that can even rupture the electrical resistor(s) 36 at the superheating zone, which leads to no longer having the defrosting function on the zone that is covered by said electrical resistor(s) 36. Furthermore, the air knife forms an insulating layer although the defrosting system is no longer adequately sized in the delamination zone, and consequently, the defrosting is inadequate in this zone.